Differential pressure sensor

Abstract

A differential MEMS pressure sensor includes a topping wafer with a top side and a bottom side, a diaphragm wafer having a top side connected to the bottom side of the topping wafer and a bottom side, and a backing wafer having a top side connected to the bottom side of the diaphragm wafer and a bottom side. The topping wafer includes a first cavity formed in the bottom side of the topping wafer. The diaphragm wafer includes a diaphragm, a second cavity formed in the bottom side of the diaphragm wafer underneath the diaphragm, an outer portion surrounding the diaphragm, and a trench formed in the top side of the diaphragm wafer and positioned in the outer portion surrounding the diaphragm.

The invention claimed is: 
     
       1. A differential MEMS pressure sensor comprising:
 a topping wafer with a top side, a bottom side, and a first cavity formed in the bottom side of the topping wafer; 
 a diaphragm wafer having a top side connected to the bottom side of the topping wafer and a bottom side, wherein the diaphragm wafer comprises:
 a diaphragm; 
 a second cavity formed in the bottom side of the diaphragm wafer underneath the diaphragm, wherein the second cavity has chamfered walls; 
 an outer portion surrounding the diaphragm, wherein the outer portion has a chamfered portion partially defined by the chamfered walls of the second cavity and a rim portion surrounding the chamfered portion; and 
 a trench formed in the top side of the diaphragm wafer and positioned in the outer portion surrounding the diaphragm, wherein the trench is positioned in the chamfered portion of the outer portion of the diaphragm wafer; and 
 
 a backing wafer having a top side connected to the bottom side of the diaphragm wafer and a bottom side. 
 
     
     
       2. The sensor of  claim 1 , wherein the trench has a first trench portion, a second trench portion, and a first gap positioned between the first trench portion and the second trench portion. 
     
     
       3. The sensor of  claim 2 , and further comprising:
 a piezoresistor on the diaphragm of the diaphragm wafer; 
 a bond pad positioned on the outer portion of the diaphragm wafer outward of the trench; and 
 an electrical trace extending from the piezoresistor on the diaphragm through the first gap in the trench to the bond pad on the outer portion. 
 
     
     
       4. The sensor of  claim 1 , wherein the topping wafer, the diaphragm wafer, and the backing wafer are silicon. 
     
     
       5. The sensor of  claim 4 , wherein the trench is formed in the diaphragm wafer using a deep reactive-ion etching process. 
     
     
       6. The sensor of  claim 1 , wherein the trench in the diaphragm wafer is in fluid communication with the first cavity in the topping wafer. 
     
     
       7. The sensor of  claim 1 , and further comprising:
 a base wafer having a top side connected to a bottom side of the backing wafer and a bottom side. 
 
     
     
       8. The sensor of  claim 7 , and further comprising:
 a first channel extending through the base wafer, the backing wafer, the diaphragm wafer, and the topping wafer and fluidly connected to the first cavity; and 
 a second channel extending through the base wafer and the backing wafer and fluidly connected to the second cavity; 
 wherein a first end of the first channel and a first end of the second channel are positioned adjacent to a center of the base wafer; and 
 wherein the first channel extends laterally outward of the first cavity, the diaphragm, and the second cavity in the backing wafer. 
 
     
     
       9. The sensor of  claim 7 , wherein the base wafer further comprises:
 a third cavity formed in the top side of the base wafer; 
 a fourth cavity formed in the top side of the base wafer; 
 a groove formed in the bottom side of the base wafer; and 
 a thin wall having a first portion between the third cavity and the groove and a second portion between the fourth cavity and the groove; 
 wherein the groove is configured to receive a portion of a pedestal on which the sensor is mounted. 
 
     
     
       10. A system comprising:
 a differential MEMS pressure sensor comprising:
 a topping wafer with a top side, a bottom side, and a first cavity formed in the bottom side of the topping wafer; 
 a diaphragm wafer having a top side connected to the bottom side of the topping wafer and a bottom side, wherein the diaphragm wafer comprises:
 a diaphragm; 
 a second cavity formed in the bottom side of the diaphragm wafer underneath the diaphragm; and 
 an outer portion surrounding the diaphragm; 
 
 a backing wafer having a top side connected to the bottom side of the diaphragm wafer and a bottom side; and 
 a base wafer having a top side connected to the bottom side of the backing wafer and a bottom side, wherein the base wafer comprises:
 a third cavity formed in the top side of the base wafer; 
 a groove formed in the bottom side of the base wafer; and 
 a thin wall formed between the third cavity and the groove; and 
 
 
 a pedestal on which the differential MEMS pressure sensor is mounted; 
 wherein the groove in the base wafer is configured to receive a portion of the pedestal. 
 
     
     
       11. The system of  claim 10 , wherein the diaphragm wafer further comprises:
 a trench formed in the top side of the diaphragm wafer and positioned in the outer portion surrounding the diaphragm. 
 
     
     
       12. The system of  claim 11 , wherein the second cavity formed in the bottom side of the diaphragm wafer has chamfered walls, wherein the outer portion of the diaphragm wafer has a chamfered portion partially defined by the chamfered walls of the second cavity and a rim portion surrounding the chamfered portion, and wherein the trench is positioned in the chamfered portion of the outer portion of the diaphragm wafer. 
     
     
       13. The system of  claim 11 , wherein the topping wafer, the diaphragm wafer, the backing wafer, and the base wafer are made out of silicon, and wherein the trench is formed in the diaphragm wafer using a deep reactive-ion etching process. 
     
     
       14. The system of  claim 11 , wherein the trench has a first trench portion, a second trench portion, and a first gap positioned between the first trench portion and the second trench portion, and wherein the differential pressure sensor further comprises:
 a piezoresistor on the diaphragm of the diaphragm wafer; 
 a bond pad positioned on the outer portion of the diaphragm wafer outward of the trench; and 
 an electrical trace extending from the piezoresistor on the diaphragm through the first gap in the trench to the bond pad on the outer portion. 
 
     
     
       15. The system of  claim 10 , and further comprising:
 a first channel extending through the base wafer, the backing wafer, the diaphragm wafer, and the topping wafer and fluidly connected to the first cavity; and 
 a second channel extending through the base wafer and the backing wafer and fluidly connected to the second cavity; 
 wherein a first end of the first channel and a first end of the second channel are positioned adjacent to a center of the base wafer; and 
 wherein the first channel extends laterally outward of the first cavity, the diaphragm, and the second cavity in the backing wafer. 
 
     
     
       16. The system of  claim 10 , and further comprising:
 a header positioned outward of and connected to the pedestal; and 
 a cap positioned around the differential MEMS pressure sensor and sealed against the header. 
 
     
     
       17. The system of  claim 10 , and further comprising:
 a fourth cavity formed in the top side of the base wafer; 
 wherein the thin wall has a first portion between the third cavity and the groove and a second portion between the fourth cavity and the groove.